Environmental laws and their resulting regulations are placing an increased emphasis on the water quality of both surface waters and ground water. Previously acceptable methods for disposing of contaminated water are now either no longer allowed or subject to strict permit requirements. Discharges of industrial wastewater, for example, must meet stringent discharge concentration limits for heavy metals such as copper, lead, nickel, mercury, cadmium, chromium VI, zinc, and silver. Other controlled pollutants include chlorofluorocarbons, pesticides, and halides. Municipalities now generally require a manufacturer to obtain a discharge permit prior to the manufacturer being allowed to discharge its waste water to a publicly owned treatment works (POTW). The permit generally places upper limits on the concentrations of the various pollutants, prohibiting discharges where the concentration of any individual critical contaminant exceeds the permitted level.
These discharge limits are ultimately defined by the water quality standards set forth by the federal government and are based on the use intended for the body of water; e.g., recreation, swimming, fishing, and drinking. Discharges from the POTW must conform to the federal standards. Consequently, industrial discharges to the POTW must not be so contaminated as to exceed the ability of the POTW to either treat the waste, reduce the concentration by dilution, or to pose a threat to the biology of the POTW. Likewise, any industry discharging directly to a stream, river, groundwater that eventually finds its way to a navigable body of water is also subject to the stringent federal clean water standards.
In an effort to meet either the POTW discharge permit requirements or the federal National Pollution Discharge Elimination System (NPDES) standards for discharge to surface bodies of water, many industrial companies pre-treat their industrial waste water prior to discharge. Generally, the waste water from all operations are piped to a end-of-pipe treatment facility wherein the pH of the combined waste water is adjusted to favor precipitation of sulfite and hydroxide salts as sodium bisulfite and/or lime is introduced to the combined waste. This pre-treatment method is inadequate for a number of reasons including: 1) more stringent discharge requirements demand concentration levels that are less than the equilibrium level of the dissolved metal using the foregoing treatment chemistries; 2) "fines" or small particles of precipitate may pass through the pre-treatment system and into the environment; 3) the mix of various metals and other contaminants make any single type of treatment a compromise, at best, since each metal has its own optimum pH and chemistries for precipitation (i.e., different metal-hydroxide solubility curves); and 4) the raw materials cost of the sodium bisulfite and lime can be very high, particularly where flow rates of waste water are high. Further, pre-treatment processes are batch processes wherein a sufficient amount of waste water is first accumulated. When a sufficient quantity of waste water has been accumulated, the precipitants are added. The batch nature of this pre-treatment process requires that large holding tanks be provided to collect the waste water, a possible back-up tank in the event the primary holding tank requires repair, and secondary containment for both tanks, since under current environmental law, spillage of industrial waste water is prohibited as an unpermitted release of a hazardous waste to the environment.
Aqueous organic streams must be remediated as well. Since pesticides and chlorofluorocarbons (CFC's) might otherwise kill the microorganisms associated with a biological treatment operation, the pesticides and CFC's must be concentrated, for example by steam distillation, with the distillate being hauled away for incineration. Other organic contaminants may be bio-remediated. The final effluent may be passed through an activated carbon column for "polishing" the pre-treated waste water thus rendering the polished waste water suitable for reuse for certain uses at the industrial site. However, the cost of periodic renewing or recharging, and eventually replacing the activated carbon, makes this operation economically less desirable than to merely discharge the pre-treated water and to purchase or manufacture "new" deionized water.
In addition to the large capital cost outlay of installing a pre-treatment facility, as well as the staffing, maintenance and operational costs associated with running the facility, there are regulatory requirements requiring a permit to operate the facility and requirements for monitoring the performance of the facility.
In many instances, clean water standards, particularly those associated with contaminated groundwater, are technology based. In other words, should a hazardous waste spill result in contamination of an underlying aquifer, remediation of the contaminated groundwater will be required until the specific contaminants are "undetectable". However, with the continuing advances made in quantitative chemical measurement instruments, the non-detectable limits are now being pushed from the parts per million range to a fraction of a part per billion. Consequently, remediation of a contaminated groundwater site that might have previously involved removal of just a few thousand gallons of water for incineration or other hazardous waste disposal, would now require removal and disposal of many millions of gallons of water. Removal and disposal of this quantity of water would be extremely cost prohibitive. Unfortunately, however, presently available technologies that enable the treatment of contaminated groundwater to achieve a level of cleanliness that will permit reinjection of the treated groundwater into the aquifer require multistage separation operations, require the removal and disposal of the separated hazardous waste, and costs many millions of dollars. What is needed is a single pass, low cost technology that will achieve the clean water standards to permit reinjection of treated groundwater back into the aquifer without having to dispose of the remediated contaminant.
A process for the direct catalytic oxidation of hydrocarbons is taught by Sen et al., U.S. Pat. No. 5,393,922. They teach the use of an externally supplied oxidizing agent, such as hydrogen peroxide, in the presence of a metallic or metal salt catalysts. In this case, an external supply of hydrogen peroxide, an extremely caustic compound, must be made available in order to perform the process. Further, the process is taught for the remediation of light organic compounds, and not for inorganic compounds and metals.
Soresen et al. Teach a method for treating polluted material such as industrial waste water involving a wet oxidation process by using an externally supplied oxidizing agent such as potassium permanganate, hydrogen peroxide, a peroxodisulphate, a hypochlorite, and the like. Also, they teach a batch process, thus significantly limiting the throughput of the process and requiring large holding tanks and large reactor.
A waste water treatment process is described by Ishii et al., U.S. Pat. No. 5,399,541, whereby organic compounds are decomposed using a two component catalyst, the first component being iron oxide and the second component being selected from a noble metal. The described process, however, requires an oxygen gas source to supply oxygen at between 1 to 1.5 the required stoichiometric amounts for complete oxidation of the organic contaminants, as well as raising the temperature of the wastewater to between 100.degree. and 370.degree. C. at a pressure sufficient to prevent boiling of the wastewater. These process conditions would necessarily entail a batch-type operation, and a complex insulated reactor and boiler system. The capital costs, and operating expense of maintaining such a system would necessarily exceed that of more conventional organic treatment systems (such as rotating biological contactors or RBCs), and would pose additional hazards due to the temperatures and pressures involved.
Accordingly, there is an escalating need for a water remediation apparatus and method that are not subject to the limitations and potential safety hazards associated with the background art; that do not require the use of additional precipitants, oxidizers, and catalysts, the use of which results in an increase the total dissolved solids (TDS) of the pre-treated effluent, or other externally supplied reagents; one that can be moved "up the pipe" prior to combining treatment incompatible waste water streams, and onto the manufacturing floor where waste water streams are segregated, and attached to process equipment for local waste water treatment to permit direct discharge from the process to the POTW without the need for pretreatment (or pretreatment permit); and one that can be fine tuned to the contaminants of interest to better able meet increasingly stringent discharge requirements.